Heat exchangers are known which include a pipe connection having a cylindrical end portion which is adapted to be coupled to a fluid flow tube by means of a clamping ring. Commonly, such a heat exchanger has two of these pipe connections, which serve as an inlet and an outlet respectively for a fluid which is arranged to flow through the heat exchanger. Where the heat exchanger is an evaporator in a vehicle air conditioning apparatus, this fluid is a refrigerant fluid for exchanging heat with a stream of air, to cool the latter before the air is admitted into the cabin of the vehicle.
In coupling devices of the known type mentioned above, the fluid flow tube is force-fitted into the cylindrical end portion of the pipe connection, and the clamping ring is then engaged axially around, and in direct contact with, the pipe connection, to grip the clamping ring on the pipe connection and to clamp the pipe connection and the end of the fluid flow tube firmly together. This gripping action includes a radial deformation of the pipe connection and also radial deformation of the fluid flow tube. These two components are thus assembled together intimately and permanently.
The clamping ring normally used is an aluminum ring having a particular profile which enables progressive radial gripping to take place, to a degree which depends on the amount by which the clamping ring is displaced axially around the pipe connection. It can however happen, in certain circumstances, that the gripping force exerted by the clamping ring is not regular, and this can lead to uncontrolled deformations of the pipe connection or the fluid flow tube or both. It can also sometimes give rise to leaks of fluid in the region of the coupling between the pipe connection and the fluid flow tube.